High speed, high density electrical connector

ABSTRACT

An electrical connector with electrically lossy materials bridging ground members. The lossy conductive members may be formed by filling a settable binder with conductive particles, allowing the partially conductive members to be formed through an insert molding process. Connectors assembled from wafers that contain signal conductors held within an insulative housing may incorporate lossy conductive members by having filled thermal plastic molded onto the insulatative housing. The lossy conductive members may be used in conjunction with magnetically lossy materials. The lossy conductive members reduce ground system do resonance within the connector, thereby increasing the high frequency performance of the connector.

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates generally to an electrical interconnectionsystems and more specifically to improved signal integrity ininterconnection systems.

2. Discussion of Related Art

Electrical connectors are used in many electronic systems. It isgenerally easier and more cost effective to manufacture a system onseveral printed circuit boards (“PCBs”) which are then connected to oneanother by electrical connectors. A traditional arrangement forconnecting several PCBs is to have one PCB serve as a backplane. OtherPCBs, which are called daughter boards or daughter cards, are thenconnected through the backplane by electrical connectors.

Electronic systems have generally become smaller, faster andfunctionally more complex. These changes mean that the number ofcircuits in a given area of an electronic system, along with thefrequencies at which the circuits operate, have increased significantlyin recent years. Current systems pass more data between printed circuitboards and require electrical connectors that are electrically capableof handling the increased bandwidth.

As signal frequencies increase, there is a greater possibility ofelectrical noise being generated in the connector in forms such asreflections, cross talk and electromagnetic radiation. Therefore, theelectrical connectors are designed to control cross-talk betweendifferent signal paths and to control the characteristic impedance ofeach signal path. Shield members are often used for this purpose.Shields are placed adjacent the signal contact elements.

Cross-talk between distinct signal paths can be controlled by arrangingthe various signal paths so that they are spaced further from each otherand nearer to a shield, which is generally a grounded plate. Thus, thedifferent signal paths tend to electromagnetically couple more to theshield and less with each other. For a given level of cross-talk, thesignal paths can be placed closer together when sufficientelectromagnetic coupling to the ground conductors are maintained.

Shields are generally made from metal components, However. U.S. Pat. No.6,709,294 (the “294 patent”), which is assigned to the same assignee asthe present application, describes making shields in a connector fromconductive plastic. The '294 patent is hereby incorporated by referencein its entirety.

Electrical connectors can be designed for single-ended signals as wellas for differential signals. A single-ended signal is carried on asingle signal conducting path, with the voltage relative to a commonreference conductor being the signal.

Differential signals are signals represented by a pair of conductingpaths, called a “differential pair.” The voltage difference between theconductive paths represents the signal. In general, the two conducingpaths of a differential pair are arranged to run near each other. Noshielding is desired between the conducting paths of the pair butshielding may be used between differential pairs.

One example of a differential pair electrical connector is shown in U.S.Pat. No. 6,293,827 (“the '827 patent”), which is assigned to theassignee of the present application. The '827 patent is incorporated byreference herein, The '827 patent discloses a differential signalelectrical connector that provides shielding with separate shieldscorresponding, to each pair of differential signals, U.S. Pat. No.6,776,659 (the '639 patent), which is assigned to the assignee of thepresent application, shows individual shields corresponding toindividual signal conductors. Ideally, each signal path is shieldedfront all other signal paths in the connector. Both the '827 patent andthe '659 patents are hereby incorporated by reference in theirentireties.

While the electrical connectors disclosed in the '827 patent and the'659 patent and other presently available electrical connector designsprovide generally satisfactory performance, the inventors of the presentinvention have noted that at high speeds for example, signal frequenciesof 1 GHz or greater, particularly above 3 GHz), electrical resonances inthe shielding system can create cross talk and otherwise degradeperformance of the connector. We have observed that such resonances areparticularly pronounced in ground systems having a shield member persignal contact or per differential pair.

My prior patent, U.S. Pat. No. 6,386,771, now published as US2004/0121652A1, which is hereby incorporated by reference in itsentirety, describes the use of lossy material to reduce unwantedresonances and improve connector performance. It would be desirable tofurther improve connector performance.

SUMMARY OF INVENTION

In one aspect, the invention relates to a wafer for an electricalconnector having a plurality of wafers. The wafer has a plurality offirst type contact elements, positioned in a column, a plurality ofdiscrete conductive elements each disposed adjacent at least one of thefirst type contact elements; insulative material securing at least theplurality of first type contact elements; and electrically lossymaterial bridging the discrete conductive elements.

In another aspect, the invention relates to an electrical connector thathas a plurality of regions. Each region has insulative material; aplurality of signal conductors, each signal conductor having a contacttail and a contact portion and an intermediate portion there between,and at least a part of the intermediate portion of each of the signalconductors secured in the insulative material; a plurality of shieldmembers, each shield member having an intermediate portion adjacent anintermediate portion of a signal conductor; and electrically lossymaterial positioned adjacent the intermediate portion of the each of theshield members.

In yet another aspect, the invention relates to an electronic systemwith a plurality of printed circuit boards, each printed circuit boardhaving a plurality of ground structures and a plurality of signaltraces. Electrical connectors are mounted to the plurality of printedcircuit boards. Each connector has a first plurality of conductingmembers, each connected to a ground structure in at least one of theplurality of printed circuit boards; a second plurality of conductingmembers, each connected to at least one of the plurality of signaltraces in at least one of the plurality of printed circuit boards, thesecond plurality of conducting members being positioned in groups withat least two conducting members of the first plurality of conductingmembers positioned adjacent conducting members of the second pluralityof conducting members in each group; and a plurality of partiallyconductive members, each connecting the at least two conducting membersof the first plurality of conducting members positioned adjacentconducting members of the second plurality of conducting members in agroup.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not ever component may be labeled in every drawing.In the drawings:

FIG. 1 is a perspective view of an electrical connector assembly showinga first electrical connector about to mate with a second electricalconnector;

FIG. 2 is an exploded view of the first electrical connector of FIG. 1,showing a plurality of wafers;

FIG. 3 is a perspective view of signal conductors of one of the wafersof the first electrical connector of FIG. 2;

FIG. 4 is a side view of the signal conductors of FIG. 3 with aninsulative housing formed around the signal conductors;

FIG. 5a is a side view of shield strips of one of the wafers of thefirst electrical connector of FIG. 2;

FIG. 5b is a perspective view of the shield strips of FIG. 5 a;

FIG. 6 is a side view of the shield strips of FIG. 5a formed on two leadframes, with each lead frame holding half of the shield strips;

FIG. 7 is a side view of the shield strips of FIG. 5a with an insulativehousing formed around the shield strips;

FIG. 8a is a perspective view of an assembled one of the wafers of thefirst electrical connector of FIG. 2;

FIG. 8b is a front view of a portion of the assembled wafer of FIG. 8 a,showing first contact ends of the signal conductors and the shieldstrips configured for connection to a printed circuit board;

FIG. 9a is a cross section to the wafer illustrated in FIG. 8a takenalong the line 9 a-9 a;

FIG. 9b is a cross section of an alternative embodiment of the wafershown in FIG. 9 a;

FIG. 9c is a cross section of an alternative embodiment of the wafershown in FIG. 9 a.

FIG. 10a is a plan view of a wafer formed according to an alternativeconstruction method;

FIG. 10b is a cross sectional view of a portion of the wafer of FIG. 10ataken along the line b-b;

FIG. 11 is a cross section view of a wafer according to an alternativeembodiment;

FIG. 12 is a cross section of a wafer formed according to a furtheralternative embodiment; and

FIG. 13 is a cross section of a wafer formed according to a furtheralternative embodiment.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” or “having,”“containing,” “involving,” and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items.

Referring to FIG. 1, there is shown an electrical connector assembly 10.The electrical connector assembly 10 includes a first electricalconnector 100 mateable to a second electrical connector 200. Electricalconnector 100 may be used as a daughter card connector and electricalconnector 200 may be used as a backplane connector. However theinvention may be broadly applied in many types of connectors.

The second electrical connector 200 may be as described in the abovereferenced U.S. Pat. No. 6,776,659.

The first electrical connector 100, which is shown in greater detail inFIGS. 2-13, includes a plurality of wafers 120, with each of theplurality of wafers 120 having a housing 122, a plurality of signalconductors 124 (see FIG. 3) and a plurality of shield strips 126 (seeFIGS. 5a and 5b ). For exemplary purposes only, the first electricalconnector 100 is illustrated with ten wafers 120, with each wafer 120having fourteen single-ended signal conductors 124 and correspondingfourteen shield strips 126. However, as it will become apparent later,the number of wafers and the number of signal conductors and shieldstrips in each wafer may be varied as desired.

The first electrical connector 100 is also shown having alignmentmodules 102 on either end, with each alignment module 102 having anopening 104 (FIG. 2) for receiving a guide pin (which may also bereferred to as a corresponding rod) 204 from member 202 of the secondelectrical connector 200. Each alignment module 102 further includesfeatures 105 (FIG. 2), 106 to engage slots in stiffeners 110, 111,respectively. Likewise, the insulative housing 122 of each wafer 120provides features 113, 114 to engage the slots in stiffeners 110 (FIG.2), 111, respectively.

Each signal conductor 124 has contact end 130 connectable to a printedcircuit board, a contact end 132 connectable to the second electricalconnector 200, and an intermediate portion 131 there between. Eachshield strip 126 (FIG. 5a ) has a first contact end 140 connectable tothe printed circuit board, a second contact end 142 connectable to thesecond electrical connector 200, and an intermediate portion 141 therebetween.

In the embodiment of the invention illustrated in FIGS. 1-8 b, the firstcontact end 130 of the signal conductors 124 includes a contact tail 133having a contact pad 133 a that is adapted for soldering to the printedcircuit board. The second contact end 132 of the signal conductors 124includes a dual beam structure 134 configured to mate to a correspondingmating structure of the second electrical connector 200. The firstcontact end 140 of the shield strips 126 includes at least two contacttails 143, 144 having contact pads 143 a, 144 a, respectively, that areadapted for soldering to the printed circuit board. The second contactend 142 of the shield strips 126 includes opposing contacting members145, 146 that are configured to provide a predetermined amount offlexibility when mating to a corresponding structure of the secondelectrical connector 200. While the drawings show contact tails adaptedfor soldering, it should be apparent to one of ordinary skill in the artthat the first contact end 130 of the signal conductors 124 and thefirst contact end 140 of the shield strips 126 may take any known form(e.g., press-fit contacts, pressure-mount contacts, paste-in-hole solderattachment) for connecting to a printed circuit board.

Still referring to FIGS. 5a and 5 b, the intermediate portion 141 ofeach shield strip 126 has a surface 141 s with a first edge 147 a and asecond edge 147 b, at least one of the first edge 147 a or the secondedge 147 b being bent out of the plane of surface 141 s. In theillustrated embodiment, the first edge 147 a is bent substantiallyperpendicular to the surface 141 s of the shield strip 126 and extendsthrough to the end of the second contact end 142 (but not through to theend of the first contact end 140).

FIG. 4 is a side view of the signal conductors 124 of FIG. 3, with thesignal conductors 124 disposed in a first insulative housing portion160. Preferably, the first insulative housing portion 160 is formedaround the signal conductors 124 by injection molding plastic. Tofacilitate this process, the signal conductors 124 are preferably heldtogether on a lead frame (not shown) as known in the art. Although notrequired, the first insulative housing portion 160 may be provided withwindows 161 adjacent the signal conductors 124. These windows 161 areintended to generally serve multiple purposes, including to: (i) ensureduring an injection molding process that the signal conductors 124 areproperly positioned, (ii) provide impedance control to achieve desiredimpedance characteristics, and (iii) facilitate insertion of materialswhich have electrical properties different than housing 160.

FIG. 7 is a side view of the shield strips 126 of FIGS. 5a and 5 b, withthe shield strips 126 disposed in a second housing portion 170. As willbe described in greater detail below, housing portion 170 may be formedfrom one or more materials that provides insulation, conductivity, lossyconductivity or magnetic lossiness.

Housing portion 170 may he formed in whole or in part by injectionmolding of material around shield strips 126. To facilitate theinjection molding process, the shield strips 126 are preferably heldtogether on two lead frames 172, 174, as shown in FIG. 6. Each leadframe 172, 174 holds every other of the plurality of the shield strips126, so when the lead frames 172, 174 are placed together, the shieldstrips 126 will be aligned as shown in FIGS. 5a and 5 b. In theembodiment shown, each lead frame 172, 174 holds a total of seven shieldstrips 126.

The lead frame 172 include tie bars 175 that connect to the secondcontact ends 142 of its respective shield strips 126 and tie bars 176that connect to the first contact ends 140 of the shield strips 126. Thelead frame 174 includes tie bars 177 that connect to the second contactends 142 of its respective shield strips 126 and tie bars 178 thatconnect to the first contact ends 140 of the shield strips 126. Thesetie bars 175-178 are cut during subsequent manufacturing processes.

The first insulative housing portion 160 may include attachment features(not shown) and the second housing portion 170 may include attachmentfeatures (not shown) that correspond to the attachment features of thefirst insulative housing portion 160 for attachment thereto. Suchattachment features may include protrusions and corresponding receivingopenings. Other suitable attachment features may also be utilized.

A first insulative housing portion 160 and the second housing portion170 may be attached to form a wafer 120. As shown in FIGS. 8a and 8b ,each signal conductor 124 is positioned along the. surface 141 sadjacent a corresponding shield strip 126. The bent edge 147 a of thesurface 141 s is directed toward the corresponding signal conductor124., The bent edge 147 a, in combination with surface 147 s, createsshielding on two sides of the adjacent signal conductor 124.

The first electrical connector 100 may also be configured to carrydifferential pairs of signals. In this configuration, the signalconductors may he organized in pairs. The surface 141 of each shieldstrip is preferably wider than the width of a pair to provide sufficientshielding to the pair.

FIG. 9a shows a water 120 in cross section taken along the line 9 a-9 ain FIG. 8a . Intermediate portions 131 of signal conductors 124 areembedded within an insulative housing 160. A portion of shield strips126 are held within housing portion 170. The shield strips 126 are heldwith first edge portions 147 a projecting between adjacent intermediateportions 131. The surface 141 s of each shield strip is held withinhousing portion 170. Housing portion 170 may be molded around shieldstrips 126 and first insulative housing 160 may he molded around signalconductors 124 prior to assembly of wafer 120.

In the illustrated embodiment, housing portion 170 is made of two typesof materials. Housing portion 170 is shown to contain a layer 910 and alayer 912. Both layers 910 and 912 may be made of a thermoplastic orother suitable binder material such that they may be molded aroundshield strips 126 to form the housing 170. Either or both of layers 910and 912 may contain particles to provide layers 910 and 912 withdesirable electromagnetic properties.

In the example of FIG. 9 a, the thermoplastic material serving as thebinder for layer 910 is filled with conducting particles. The fillersmake layer 910 “electrically lossy.”

Materials that conduct, but with some loss, over the frequency range ofinterest are referred to herein generally as “electrically lossy”materials. Electrically lossy materials can be formed from lossydielectric and/or lossy conductive materials. The frequency range ofinterest depends on the operating parameters of the system in which tosuch as connector is used, but will generally be between about 1 GHz and25 GHz, though higher frequencies or lower frequencies may be ofinterest in some applications. Some connector designs may have frequencyranges of interest that span only a portion of this range, such as 1 to10 GHz or 3 to 15 GHz.

Electrically lossy material can be formed from material traditionallyregarded as dielectric materials, such as those that have an electricloss tangent greater than approximately 0.01 in the frequency range ofinterest. The “electric loss tangent” is the ratio of the imaginary partto the real part of the complex electrical permittivity of the material.Examples of materials that may he used are those that have an electricloss tangent between approximately 0.04 and 0.2 over a frequency rangeof interest.

Electrically lossy materials can also be formed from materials that aregenerally thought of as conductors, but are either relatively poorconductors over the frequency range of interest, contain particles orregions that are sufficiently dispersed that they do not provide highconductivity or otherwise are prepared with properties that lead to arelatively weak bulk conductivity over the frequency range of interest.

Electrically lossy materials may be partially conductive materials, suchas those that have a surface resistivity between 1 Ω/square and 10⁶Ω/square. In some embodiments, the electrically lossy material has asurface resistivity between 1 Ω/square and 10³ Ω/square. In someembodiments, the electrically lossy material has a surface resistivitybetween 10 Ω/square and 100 Ω/square. As a specific example, thematerial may have a surface resistivity of between about 20 Ω/square and40 Ω/square.

In some embodiments, electrically lossy material is formed by adding afiller that contains conductive particles to a binder. Examples ofconductive particles that may be used as a filler to form anelectrically lossy materials include carbon or graphite formed asfibers, flakes or other particles. Metal in the form of powder, flakes,fibers or other particles may also be used to provide suitableelectrically lossy properties. Alternatively, combinations of fillersmay be used. For example, metal plated carbon particles may be used.Silver and nickel are suitable metal plating for fibers. Coatedparticles may be used alone or in combination with other fillers, suchas carbon flake.

The binder or matrix may be any material that will set, cure or canotherwise be used to position the tiller material. In some embodiments,the binder may be a thermoplastic material such as is traditionally usedin the manufacture of electrical connectors to facilitate the molding ofthe electrically lossy material into the desired shapes and locations aspart of the manufacture of the electrical connector. However, manyalternative forms of binder materials may be used. Curable materials,such as epoxies, can serve as a binder. Alternatively, materials such asthermosetting, resins or adhesives may be used. Also, while the abovedescribed binder material are used to create an electrically lossymaterial by forming a binder around conducting particle fillers, theinvention is not so limited. For example, conducting particles may beimpregnated into a formed matrix material. As used herein, the term“binder” encompasses a material that encapsulates the filler or isimpregnated with the filler.

Preferably, the fillers will be present in a sufficient volumepercentage to allow conducting paths to be created from particle toparticle. For example, when metal fiber is used, the fiber may bepresent in about 1% to 40% by volume. The amount of filler may impactthe conducting properties of the material.

In one contemplated embodiment, layer 910 has a thickness between 1 and40 mils (about 0.025 mm to 1 mm). The bulk resistivity of layer 910depends on its thickness as well as its surface resistivity. The bulkresistivity is suitable to allow the layer to provide some conduction,but with some loss. Bulk resistivity of an electrically lossy structureused herein may be between about 0.01 Ω-cm and 1 Ω-cm. In someembodiments, the bulk resistivity is between about 0.05 Ω-cm and 0.5Ω-cm. In some embodiments, the bulk resistivity is between about 0.1Ω-cm and 0.2 Ω-cm.

Layer 912 provides a magnetically lossy layer. Layer 912 may, like layer910, be formed of a binder or matrix material with fillers. In thepictured embodiment, layer 912 is made by molding a filled bindermaterial. The binder for layer 912 may be the same as the binder usedfor layer 910 or any other suitable binder. Layer 912 is filled withparticles that provide that layer with magnetically lossycharacteristics. The magnetically lossy particles may be in anyconvenient form, such as flakes or fibers. Ferrites are commonmagnetically lossy materials. Materials such as magnesium ferrite,nickel ferrite, lithium ferrite, yttrium garnet or aluminum garnet maybe used.

The “magnetic loss tangent” is the ratio of the imaginary part to thereal part of the complex magnetic permeability of the material.Materials with higher loss tangents may also be used. Ferrites willgenerally have a loss tangent above 0.1 at the frequency range ofinterest. Presently preferred ferrite materials have a loss tangentbetween approximately 0.1 and 1.0 over the frequency range of 1 Ghz to 3GHz and more preferably a magnetic loss tangent above 0.5.

It is possible that a material may simultaneously be a lossy dielectricor a lossy conductor and a magnetically lossy material. Such materialscan be formed, for example, by using magnetically lossy fillers that arepartially conductive or by using a combination of magnetically lossy andelectrically lossy fillers.

Layer 912 plays the role of absorptive material as described in my priorU.S. Pat. No. 6,786,771, which is incorporated herein by reference.Layer 912 reduces resonance between shields in adjacent wafers 120.

Layer 910 provides “bridging” between the individual shield strips 126within the wafer 120. The bridging provides an electrically lossy pathbetween conducting, members over the frequency range of interest. Thebridging may be provided by a physical connection to the conductingmembers that are bridged. In addition, over the frequency range ofinterest, signals may couple between structures capacitively orotherwise without direct physical contact between the structures.Accordingly, “bridging” may not require direct physical contact betweenstructures.

With bridging in place, each of the shield strips 126 is less likely toresonate independently from the others. Preferably, layer 910 issufficiently conductive that the individual shield strips do notresonate independently but sufficiently lossy that the shield strips andthe bridging do not form a combined structure that, in combination withsimilar structures in another wafer, support resonant modes betweenadjacent wafers.

FIG. 9b shows an alternative embodiment of the wafer 120. In wafer 120′,intermediate portions 131 of signal conductors 124 and shield strips 126are held within an insulative housing 160′. Insulative housing 160′ maybe formed in any convenient manner. It may be formed in a single moldingstep or in multiple molding steps. Layer 914 is formed on top ofinsulative housing 160′. Layer 914 is an electrically lossy layersimilar to layer 910.

In contrast to layer 910, surfaces 141 s of shield strips 126 are notembedded in layer 914. In the embodiment shown, surfaces 141 s are notin direct contact with layer 914. The surfaces 141 s are separated fromlayer 914 by a small portion of insulative housing 160′. Each of thesurfaces 141 s is capacitively coupled to layer 914. In this way, layer914 provides a partially conductive path at the frequencies of interestbridging the individual shield strips 126 in wafer 120′. Similar to theconfiguration in FIG. 9a , partially conductive layer 914 reducesresonances between the shield strips 126 within wafer 120′.

Water 120′ may optionally be formed with a magnetically lossy material,such as a layer 912 shown in FIG. 9 a.

FIG. 9c shows a further embodiment. Wafer 120″ includes an insulativehousing 160 as shown in FIG. 9 a. Surfaces 141 s of the shield strips126 are held within a partially conductive layer 916. Layer 916 may be apartially conductive layer formed in the same fashion as layer 910,thereby bridging the shield strips 126. Regions 918 within layer 916 areformed from magnetically lossy material. Regions 918 may be formed ofthe same material as is used to form layer 912. Regions 918 may beformed in a separate step or may be formed by adding magnetically lossyparticles during the formation of layer 916.

FIGS. 9a and 9c show the use of electrically lossy and magneticallylossy materials in combination. In the described embodiments, both themagnetically lossy and electrically lossy materials are formed by theaddition of particles to a binder. It is not necessary that theparticles be added to binders forming distinct structures. For example,magnetically lossy and conductive particles may be intermixed in asingle layer, such as layer 914, shown in FIG. 9 b.

It is also not necessary that bridging between shield strips in a waferbe formed from particles encapsulated in the binder. FIG. 10a shows analternative construction of a wafer 120′″. Wafer 120′″ has inserts 950 aand 950 b inserted in openings in a surface of wafer 120′″. Preferably,the openings are sufficiently deep that they expose surfaces 141 s ofthe shield strips within the wafer.

FIG. 10b shows a cross section of a portion of wafer 120′″ taken alongthe line b-b in FIG. 10 a. In FIG. 10 b, insert 950 a is seen incross-section. Insert 950 a may, for example, be a lossy conductivecarbon filled adhesive preform such as those sold by Techfilm ofBillerica, Mass., U.S.A. This preform includes an epoxy binder 952filled with carbon flakes. The binder surrounds carbon fiber 956, whichacts as a reinforcement for the preform. When inserted in a wafer 120′″,preform 950 a adheres to shield strips 126. In this embodiment, preform950 a adheres through the adhesive in the preform, which is cured in aheat treating process. Preform 950 a thereby provides electrically lossbridging between the shield strips. Various forms of reinforcing fiber,in woven or non-woven form, may be used. Non-woven carbon fiber is onesuitable material.

In alternative embodiments, the preforms could be made to include bothconductive and magnetically lossy filler. The conductive andmagnetically lossy filler may be intermixed in a continuous binderstructure or may be deposited in layers.

Electrically loss materials may also be used in connectors that do nothave ground strips. FIG. 11 shows in cross-section an example of a wafer1120 that includes signal conductors with intermediate portions 131embedded in the insulative housing 1160. Wafer 1120 is designed forapplications in which alternating signal conductors are connected toground forming what it is sometimes referred to as a “checkerboardpattern.” For example, signal conductor 1126 is intended to be connectedto ground. In wafer 1120, a partially conductive layer 1170 is used toprovide bridging between signal conductors 1126 that are grounded. Layer1170 may be formed generally in the same fashion as layers 910 or 914.

FIG. 12 shows a wafer 1220 designed for carrying differential signals.Wafer 1212 includes an insulative housing 1260. Signal conductors suchas 1231 a and 1231 b are arranged in pairs within insulative housing1260. Shield members 1226 separate the pairs. Shield strips 1226 areembedded in a housing 1270. In wafer 1220, housing 1270 includes apartially conductive layer 1210 and a magnetically lossy layer 1212.Layers 1012 and 1210 may be formed generally as layers 910 and 912described above in connection with FIG. 9 a.

FIG. 13 shows as further embodiment of a wafer 1320 that may be used toform an electrical connector as pictured in FIG. 1. Wafer 1320 may besimilar to wafer 1120. It contains a plurality of conductors 131 held inan insulative housing 1360. However, none of the signal conductors 131in wafer 1320 is specifically designed to be connected to ground.

Layer 1370 is an electrically lossy material, it bridges all of thesignal conductors 131. Where the benefit of reducing resonances betweenthe signal conductors acting as grounds outweighs any loss of signalintegrity caused by attenuation of the signals carried on conductors,layer 1370 provides a net positive impact on the signal integrity of aconnector formed with wafers 1370.

In embodiments such as those shown in FIGS. 9b and 13 in which thebridging material is not in direct contact with structures serving asground contacts, there may be no direct electrical connection betweenthe electrically lossy material and ground. Such a connection is notrequired, though may be included in some applications.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art.

As one example, it is described that bridging may be provided bycapacitively coupling an electrically lossy member to two structures.Because no direct conducting path need be provided, it is possible thatthe electrically lossy material may be discontinuous, with electricallyinsulating material between segments of electrically lossy material.

Alternatively, electrically lossy bridging may be formed by creating,signal paths that include conductive and lossy materials. For example,FIG. 1 shows a lossy layer 1170 that has vertical portions 1150 adjacentconductors 1126 and a horizontal portion 1152 joining the verticalportions. Portions 1150 and 1152 in combination create an electricallylossy path between contacts 1126. On or the other of these portions maybe formed from a conductive material, such as metal. For example,portions 1150 may be electrically lossy material molded into housing1160 and portion 1152 may be implemented as a metal plate. Thoughportion 1152 would be conductive, the signal path between adjacentcontacts 1126 would be electrically lossy.

Further, example embodiments show each of the signal conductors andground conductors molded in an insulative housing, such as plastic.However, air is often a suitable dielectric and may be preferable toplastic in some applications. In some embodiments, the conductors withinthe wafer will be held in an insulative plastic housing over arelatively small portion of their length and surrounded by air, or otherdielectric material, over the remainder of their length.

As another example, electrically lossy structures and magnetically lossystructures were described as being formed by embedding particles in asettable binder. Where molding is used, preferably features are providedin each region formed by a to separate molding step to interlock theregions.

Partially conductive structures may be formed in any convenient manner.For example, adhesive substances which are inherently partiallyconductive may be applied to shield strips through windows in aninsulative housing. As another alternative, conducting filaments such ascarbon fibers may be overlaid on shield members before they are moldedinto a housing or they may be attached to the shield members withadhesive after the shield members are in place.

Further, lossy conductive material is shown m planar layers. Such astructure is not required. For example, partially conductive regions maybe positioned only between shield strips or only between selectiveshield strips such as those found to be most susceptible to resonances.

Also, it was described that wafers 120 are formed by attaching asubassembly containing signal contacts to a subassembly containingshield members. It is not necessary that the sub-assemblies be securedto each other. However, where desired, the sub-assemblies may be securedwith various features including snap fit features or features thatengage through function.

Further, electrically and magnetically lossy materials are shown only inconnection with a daughter card connector. However, benefits of usingsuch materials is not limited to use in daughter card connectors. Suchmaterials may be used in backplane connectors or in other types ofconnectors, such as cable connectors, stacking connectors, mezzanineconnectors. The concepts may also be applied in connectors other thanboard to board connectors. Similar concepts may be applied in chipsockets in other types of connectors.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andscope of the invention. Accordingly, the foregoing description anddrawings, are by way of example only.

What is claimed is:
 1. A wafer for an electrical connector having aplurality of wafers, the wafer comprising: a) a plurality of first typecontact elements, positioned in a column; b) a plurality of discreteconductive elements each disposed adjacent at least c) insulativematerial securing at least the plurality of first type contact elements;and d) electrically lossy material bridging the discrete conductiveelements.
 2. The wafer of claim 1 wherein the electrically lossymaterial comprises a lossy conductor.
 3. The wafer of claim 1 whereinthe electrically lossy material comprises a lossy dielectric.
 4. Thewafer of claim 1 wherein the electrically lossy material bridges theconductive elements by making direct contact with each of the discreteconductive elements.
 5. The wafer of claim 1 wherein the electricallylossy material bridges the conductive elements of being capacitivelycoupled to each of the discrete conductive elements.
 6. The wafer ofclaim 1 wherein the electrically lossy material comprises a binder and aplurality of conducting particles therein.
 7. The wafer of claim 6wherein the conducting particles comprise flakes.
 8. The wafer of claim6 wherein the conducting particles comprises fibers.
 9. The wafer ofclaim 8 wherein the fibers comprise metal coated fibers.
 10. The waferof claim 9 wherein the fibers comprise of nickel coated graphite fibers.11. The wafer of claim 6 wherein the binder is thermoplastic.
 12. Thewafer of claim 6 wherein the binder is a curable adhesive.
 13. The waferof claim 1 wherein the electrically lossy material comprises of preformhaving a fibrous substrate, a binder and a plurality of conductiveparticles disposed in the binder.
 14. The wafer of claim 1 wherein theelectrically lossy material has a surface resistance of between 1 and10³ Ω/square.
 15. The wafer of claim 1 wherein the electrically lossymaterial has a surface resistance between 10 Ω/square and 100 Ω/square.16. The wafer of claim 1 wherein the electrically lossy material has asurface resistance between 20 Ω/square and 40 Ω/square.
 17. The wafer ofclaim 14 wherein the electrically lossy material has a thickness between0.25 mm and 1 mm in a region adjacent each of the conductive elements.18. The wafer of claim 1 wherein the electrically lossy material has abulk resistance of between 0.01 Ω-cm and 1 Ω-cm.
 19. The wafer of claim1 wherein the electrically lossy material has a bulk resistance between0.05 Ω-cm and 0.5 Ω-cm.
 20. The wafer of claim 1 wherein theelectrically lossy material has a bulk resistance between 0.1 Ω-cm and0.2 Ω-cm. 21-51. (canceled)